So first let’s look at polarization in general. You can think of light as traveling in waves. One way to visualize these waves is to imagine taking a length of rope and tying one end to a post. Moving the free end up and down sets up a “wave” along the rope which also moves up and down. If you think of the rope as representing a beam of light, the light would be “vertically polarized”.
You could also move the free end around in a circle and, if you got the timing just right, you could set up a wave that looks like a corkscrew. This is analogous to a light beam having circular polarization.